Although sunbathing is frequently performed for improvement of health, it is known that erythema is formed by excessively exposing the skin to sunlight and that this phenomenon is caused mainly by light beam of a wavelength of 280 to 320 nm, so-called UV-B. For the purpose of prevention of occurrence of such a burn symptom, it is proposed to compound ultraviolet absorber having absorption in the region of UV-B (Please refer to the gazette of Japanese Patent Publication No. 39404/1984 and the specification of the corresponding U.S. Pat. No. 4,061,730).
On the other hand, it has been thought that light beam having a wavelength of 320 to 400 nm (UV-A), which makes the skin brown without causing erythema, is a desirable light. However, it has been revealed that while UV-B reaches only up to the epithelial layer, UV-A reaches up to the dermal layer, a deeper layer, and therefore, aging of skin is accelerated by long-term exposure to UV-A.
Therefore, cosmetics wherein a compound having an absorption band in the region of UV-A is compounded have come to be eagerly sought, and substituted dibenzoylmethanes have been proposed as compounds having such effects (Please refer to the gazette of Japanese Patent Publication No. 4813/1986 and the specification of U.S. Pat. No. 4,489,057). However, the substituted dibenzoylmethanes cannot exhibit sufficient effect since their absorption ability rapidly decreases at 350 nm or more. Further, their water resisting stability is not sufficient and improvement in sustainability of effect has been desired.
Further, the specification of U.S. Pat. No. 4,446,262 discloses a light-stabilized polymer composition containing an ultraviolet absorber compound represented by the following formula (I) ##STR1## wherein X.sup.1 is 1,2-phenylene, 1,2-naphthylene, 2,3-naphthylene, a group represented by the following formula (a) ##STR2## (wherein, R is --O--, --CO--, --S--, --SO.sub.2 --, --CH.sub.2 -- or CH.sub.2).sub.2 -- or --C(CH.sub.3).sub.2 --) or a group represented by the following formula (b) ##STR3## (wherein, R is as defined above);
n is 1, 2 or 3; and R.sup.1 is a n-valent hydrocarbon. This composition aims at using the above compound as protection against deterioration, due to exposure to ultraviolet ray, of the polymer base material itself, for example, thermoplastic resin such as polyester, polyamide, polycarbonate, polyolefin, polyether or polysulfone, or thermosetting resin such as phenolformaldehyde resin, melamine resin, polyurethane resin, epoxy resin or unsaturated polyester resin. This U.S. Patent specification has no disclosure about a cosmetic composition directed to a protective object utterly different from protection of polymer base material itself.
An object of this invention is to provide an ultraviolet ray-absorbing cosmetic composition for application to skin.
Another object of the invention is to provide an ultraviolet ray-absorbing cosmetic composition containing a cyclic imino ester compound which is not only sufficiently safe when it is directly applied onto the skin of human beings, but also colorless, odorless and non-irritating.
Still another object of the invention is to provide an ultraviolet ray-absorbing cosmetic composition which is non-volatile, has a chemically stable property not to decompose by sweating or washing, and moreover is stable against sunlight and sustains its ultraviolet ray-absorbing ability over a long time.
Still another object of the invention is to provide a method for protection of sites of human skin from ultraviolet ray using the cosmetic composition of the invention.